TypeScript

What it is

TypeScript is a superset of JavaScript that adds optional static types. All valid JavaScript is valid TypeScript, but TypeScript allows declaring types that the compiler verifies before execution, catching errors in development instead of production.

Why TypeScript?

Errors detected at compile time, not runtime
Intelligent IDE autocomplete
Safe refactoring at scale
Implicit documentation in types
De facto standard for serious JavaScript projects

Key features

Interfaces and types: define data shapes
Generics: reusable parameterized types
Union types: string | number
Type inference: compiler deduces types automatically
Strict mode: maximum type safety

TypeScript in the ecosystem

React: typed JSX, typed props
Next.js: native support
AWS CDK: typed infrastructure
Node.js: typed backend

Configuring `strict`

Strict mode enables all type checks. It is the recommended configuration for new projects:

{
  "compilerOptions": {
    "strict": true,
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "esModuleInterop": true,
    "skipLibCheck": true,
    "outDir": "dist"
  }
}

Individual flags that strict enables:

Flag	What it prevents
`strictNullChecks`	Accessing `null`/`undefined` without checking
`noImplicitAny`	Variables without explicit or inferred type
`strictFunctionTypes`	Incorrect contravariant function parameters
`strictPropertyInitialization`	Uninitialized class properties
`noImplicitThis`	Using `this` without a known type

When NOT to use TypeScript

One-off scripts (bash or Python are faster)
Throwaway prototypes where iteration speed matters more than correctness
Projects where the team has no experience with static types (the learning curve is real)

Why it matters

TypeScript turns runtime errors into compile-time errors. In projects of any size, the type system acts as living documentation, enables safe refactoring, and reduces the most common category of bugs: type errors.

References

TypeScript Documentation — Official documentation.
TypeScript Handbook — Complete guide.
TypeScript Playground — Microsoft, 2024. Interactive environment for experimenting with TypeScript.